The products are manufactured or distributed by CVS, Hyland’s Homeopathic and other companies and are sold online and in retail stores. Seizures, lethargy and other problems have been reported in children using the products.

CVS has voluntarily withdrawn the products, and Hyland’s has issued a statement saying that it is “fully cooperating with the F.D.A.’s inquiry.”

The F.D.A. issued a similar warning in 2010, saying that the products contain “inconsistent amounts” of belladonna, a plant compound that can be dangerous at high doses. At that time, Hyland’s recalled its products, changed the formula and then began selling them again in 2011.

The current F.D.A. warning does not mention belladonna or other specific components of the products as posing health risks. Hyland’s statement said that the amount of belladonna in the product is two-trillionths of a gram per tablet and that “a child would have to eat multiple bottles at once to experience the first side effect of belladonna, which is typically dry mouth.”

An F.D.A. spokeswoman, Lyndsay Meyer, said that the agency is “currently investigating this issue, including testing product samples and analyzing the adverse-event reports.”